Diamond nitrogen vacancy sensed ferro-fluid hydrophone

ABSTRACT

Systems and apparatuses are disclosed for a hydrophone using a nitrogen vacancy center diamond magnetic sensor.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is related to co-pending U.S. application Ser.No. __/___,______, filed Jan. 21, 2016, titled “HYDROPHONE,” Atty. Dkt.No. 111423-1071, which is incorporated by reference herein in itsentirety.

FIELD BACKGROUND

The present invention relates generally to a hydrophone using a magneticsensor.

Typical hydrophones use ceramics or other solid-state materials. Soundwaves in the surrounding water strike the surface of the material andtransfer momentum before the sound can be sensed. A loss of signal canincur due to the large mismatch of material properties. This loss ofsignal can result in lower sensitivity which limits the performance ofthe hydrophone. The large mismatch in material composition and state ofmatter, e.g., solid versus liquid, results in additional unintentionalfiltering of the signal and signal refraction.

SUMMARY

Systems and hydrophone apparatuses are disclosed. In one implementation,a hydrophone includes a ferro-fluid that deforms when contacted by soundwaves. A magnet is used to activate the ferro-fluid. One or more diamondnitrogen vacancy (DNV) sensors detect the magnetic field and movement ofthe ferro-fluid. For example, the movement of the ferro-fluid changesthe magnetic field of the ferro-fluid which can be detected. The changesin the magnetic field can then be used to determine the movement of theferro-fluid. An electronic processor can translate movement of theferro-fluid into acoustic data associated with the sound waves. In otherimplementations, the hydrophone can be installed within or as part of avehicle. Further, the ferro-fluid can be enclosed in a membrane that isused to contain the ferro-fluid.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other features of the present disclosure will becomemore fully apparent from the following description and appended claims,taken in conjunction with the accompanying drawings. Understanding thatthese drawings depict only several implementations in accordance withthe disclosure and are, therefore, not to be considered limiting of itsscope, the disclosure will be described with additional specificity anddetail through use of the accompanying drawings.

FIG. 1 illustrates one orientation of an NV center in a diamond lattice.

FIG. 2 is an energy level diagram illustrates energy levels of spinstates for the NV center.

FIG. 3 is a schematic illustrating an NV center magnetic sensor system.

FIG. 4 is a graph illustrating the fluorescence as a function of appliedRF frequency of an NV center along a given direction for a zero magneticfield and a non-zero magnetic field.

FIG. 5 is a graph illustrating the fluorescence as a function of appliedRF frequency for four different NV center orientations for a non-zeromagnetic field.

FIG. 6 is a schematic illustrating an NV center magnetic sensor systemin accordance with some illustrative implementations.

FIG. 7 is a schematic illustrating a hydrophone in accordance with someillustrative implementations.

FIG. 8 is a schematic illustrating a portion of a vehicle with ahydrophone in accordance with some illustrative implementations.

FIG. 9 is a schematic illustrating a portion of a vehicle with ahydrophone with a containing membrane in accordance with someillustrative implementations.

FIG. 10 is a schematic illustrating a portion of a vehicle with ahydrophone in accordance with some illustrative implementations.

FIG. 11 is a schematic illustrating a portion of a vehicle with ahydrophone with a containing membrane in accordance with someillustrative implementations.

DETAILED DESCRIPTION

Nitrogen-vacancy (NV) centers are defects in a diamond's crystalstructure. Synthetic diamonds can be created that have these NV centers.NV centers generate red light when excited by a light source, such as agreen light source, and microwave radiation. When an excited NV centerdiamond is exposed to an external magnetic field the frequency of themicrowave radiation at which the diamond generates red light and theintensity of the light change. By measuring this change and comparingthe change to the microwave frequency that the diamond generates redlight at when not in the presence of the external magnetic field, theexternal magnetic field strength can be determined. Accordingly, NVcenters can be used as part of a magnetic field sensor. In variousimplementations, a magnetic field sensor using a NV center diamond canbe used in a hydrophone. The hydrophone can contain a ferromagneticliquid and the DNV sensor can sense changes in the magnetic field of theferromagnetic fluid due to disturbances of the ferromagnetic fluidcaused by sound waves that contact the ferromagnetic fluid.

In various implementations, microwave RF excitation is needed in a DNVsensor. The more uniform the microwave signal is across the NV centersin the diamond the better and more accurate an NV sensor will perform.Uniformity, however, can be difficult to achieve. Also, the larger thebandwidth of the element, the better the NV sensor will perform. Largebandwidth, such as octave bandwidth, however, can be difficult toachieve. Various NV sensors respond to a microwave frequency that is noteasily generated by RF antenna elements that are comparable to the smallsize of the NV sensor. In addition, RF elements should reduce the amountof light within the sensor that is blocked by the RF elements. When asingle RF element is used, the RF element is offset from the NV diamondwhen the RF element maximized the faces and edges of the diamond thatlight can enter or leave. Moving the RF element away from the NVdiamond, however, impacts the uniformity of strength of the RF that isapplied to the NV diamond.

The present inventors have realized that a DNV sensor could be used incombination with a ferro-fluid to create a hydrophone that does notsuffer from the loss of sensitivity caused by the mismatch of materialcomposition. The disclosed hydrophone has a liquid-to-liquid interfacerather than a solid-to-liquid interface. As sound waves contact theferro-fluid, the shape of the ferro-fluid will change. One or more DNVsensors can be used to detect this movement. The movement of theferro-fluid can then be translated into acoustic measurements.

NV Center, Its Electronic Structure, and Optical and RF Interaction

The nitrogen vacancy (NV) center in diamond comprises a substitutionalnitrogen atom in a lattice site adjacent a carbon vacancy as shown inFIG. 1. The NV center may have four orientations, each corresponding toa different crystallographic orientation of the diamond lattice.

The NV center may exist in a neutral charge state or a negative chargestate. Conventionally, the neutral charge state uses the nomenclatureNV⁰, while the negative charge state uses the nomenclature NV, which isadopted in this description.

The NV center has a number of electrons including three unpairedelectrons, each one from the vacancy to a respective of the three carbonatoms adjacent to the vacancy, and a pair of electrons between thenitrogen and the vacancy. The NV center, which is in the negativelycharged state, also includes an extra electron.

The NV center has rotational symmetry, and as shown in FIG. 2, has aground state, which is a spin triplet with ³A₂ symmetry with one spinstate m_(s)=0, and two further spin states m_(s)=+1, and m_(s)=−1. Inthe absence of an external magnetic field, the m_(s)=±1 energy levelsare offset from the m_(s)=0 due to spin-spin interactions, and them_(s)=±1 energy levels are degenerate, i.e., they have the same energy.The m_(s)=0 spin state energy level is split from the m_(s)=±1 energylevels by an energy of 2.87 GHz for a zero external magnetic field.

Introducing an external magnetic field with a component along the NVaxis lifts the degeneracy of the m_(s)=±1 energy levels, splitting theenergy levels m_(s)=±1 by an amount 2gμ_(B)Bz, where g is the g-factor,μ_(B) is the Bohr magneton, and Bz is the component of the externalmagnetic field along the NV axis. This relationship is correct for afirst order and inclusion of higher order corrections is a straightforward matter and will not affect the computational and logic steps inthe systems and methods described below.

The NV center electronic structure further includes an excited tripletstate ³E with corresponding m_(s)=0 and m_(s)=±1 spin states. Theoptical transitions between the ground state ³A₂ and the excited triplet³E are predominantly spin conserving, meaning that the opticaltransitions are between initial and final states which have the samespin. For a direct transition between the excited triplet ³E and theground state ³A₂, a photon of red light is emitted with a photon energycorresponding to the energy difference between the energy levels of thetransitions.

There is, however, an alternate non-radiative decay route from thetriplet ³E to the ground state ³A₂ via intermediate electron states,which are thought to be intermediate singlet states A, E withintermediate energy levels. Significantly, the transition rate from them_(s)=±1 spin states of the excited triplet ³E to the intermediateenergy levels is significantly greater than the transition rate from them_(s)=0 spin state of the excited triplet ³E to the intermediate energylevels. The transition from the singlet states A, E to the ground statetriplet ³A₂ predominantly decays to the m_(s)=0 spin state over them_(s)=±1 spin states. These features of the decay from the excitedtriplet ³E state via the intermediate singlet states A, E to the groundstate triplet ³A₂ allows that if optical excitation is provided to thesystem, the optical excitation will eventually pump the NV center intothe m_(s)=0 spin state of the ground state ³A₂. In this way, thepopulation of the m_(s)=0 spin state of the ground state ³A₂ may be“reset” to a maximum polarization determined by the decay rates from thetriplet ³E to the intermediate singlet states.

Another feature of the decay is that the fluorescence intensity due tooptically stimulating the excited triplet ³E state is less for them_(s)=±1 states than for the m_(s)=0 spin state. This is so because thedecay via the intermediate states does not result in a photon emitted inthe fluorescence band, and because of the greater probability that them_(s)=±1 states of the excited triplet ³E state will decay via thenon-radiative decay path. The lower fluorescence intensity for them_(s)=±1 states than for the m_(s)=0 spin state allows the fluorescenceintensity to be used to determine the spin state. As the population ofthe m_(s)=±1 states increases relative to the m_(s)=0 spin, the overallfluorescence intensity will be reduced.

NV Center, or Magneto-Optical Defect Center, Magnetic Sensor System

FIG. 3 is a schematic illustrating a NV center magnetic sensor system300 which uses fluorescence intensity to distinguish the m_(s)=±1states, and to measure the magnetic field based on the energy differencebetween the m_(s)=+1 state and the m_(s)=−1 state. The system 300includes an optical excitation source 310, which directs opticalexcitation to an NV diamond material 320 with NV centers. The system 300further includes an RF excitation source 330 which provides RF radiationto the NV diamond material 320. Light from the NV diamond may bedirected through an optical filter 350 to an optical detector 340.

The RF excitation source 330 may be a microwave coil, for example. TheRF excitation source 330 when emitting RF radiation with a photon energyresonant with the transition energy between ground m_(s)=0 spin stateand the m_(s)=+1 spin state excites a transition between those spinstates. For such a resonance, the spin state cycles between groundm_(s)=0 spin state and the m_(s)=+1 spin state, reducing the populationin the m_(s)=0 spin state and reducing the overall fluorescence atresonance. Similarly resonance occurs between the m_(s)=0 spin state andthe m_(s)=−1 spin state of the ground state when the photon energy ofthe RF radiation emitted by the RF excitation source is the differencein energies of the m_(s)=0 spin state and the m_(s)=−1 spin state. Atresonance between the m_(s)=0 spin state and the m_(s)=−1 spin state, orbetween the m_(s)=0 spin state and the m_(s)=+1 spin state, there is adecrease in the fluorescence intensity.

The optical excitation source 310 may be a laser or a light emittingdiode, for example, which emits light in the green, for example. Theoptical excitation source 310 induces fluorescence in the red, whichcorresponds to an electronic transition from the excited state to theground state. Light from the NV diamond material 320 is directed throughthe optical filter 350 to filter out light in the excitation band (inthe green for example), and to pass light in the red fluorescence band,which in turn is detected by the detector 340. The optical excitationlight source 310, in addition to exciting fluorescence in the diamondmaterial 320, also serves to reset the population of the m_(s)=0 spinstate of the ground state ³A₂ to a maximum polarization, or otherdesired polarization.

For continuous wave excitation, the optical excitation source 310continuously pumps the NV centers, and the RF excitation source 330sweeps across a frequency range which includes the zero splitting (whenthe m_(s)=±1 spin states have the same energy) photon energy of 2.87GHz. The fluorescence for an RF sweep corresponding to a diamondmaterial 320 with NV centers aligned along a single direction is shownin FIG. 4 for different magnetic field components Bz along the NV axis,where the energy splitting between the m_(s)=−1 spin state and them_(s)=+1 spin state increases with Bz. Thus, the component Bz may bedetermined. Optical excitation schemes other than continuous waveexcitation are contemplated, such as excitation schemes involving pulsedoptical excitation, and pulsed RF excitation. Examples, of pulsedexcitation schemes include Ramsey pulse sequence, and spin echo pulsesequence.

In general, the diamond material 320 will have NV centers aligned alongdirections of four different orientation classes. FIG. 5 illustratesfluorescence as a function of RF frequency for the case where thediamond material 320 has NV centers aligned along directions of fourdifferent orientation classes. In this case, the component Bz along eachof the different orientations may be determined. These results alongwith the known orientation of crystallographic planes of a diamondlattice allows not only the magnitude of the external magnetic field tobe determined, but also the direction of the magnetic field.

While FIG. 3 illustrates an NV center magnetic sensor system 300 with NVdiamond material 320 with a plurality of NV centers, in general themagnetic sensor system may instead employ a different magneto-opticaldefect center material, with a plurality of magneto-optical defectcenters. The electronic spin state energies of the magneto-opticaldefect centers shift with magnetic field, and the optical response, suchas fluorescence, for the different spin states is not the same for allof the different spin states. In this way, the magnetic field may bedetermined based on optical excitation, and possibly RF excitation, in acorresponding way to that described above with NV diamond material.

FIG. 6 is a schematic of an NV center magnetic sensor 600, according toan embodiment of the invention. The sensor 600 includes an opticalexcitation source 610, which directs optical excitation to an NV diamondmaterial 620 with NV centers, or another magneto-optical defect centermaterial with magneto-optical defect centers. An RF excitation source630 provides RF radiation to the NV diamond material 620. The NV centermagnetic sensor 600 may include a bias magnet 670 applying a biasmagnetic field to the NV diamond material 620. Light from the NV diamondmaterial 620 may be directed through an optical filter 650 and anelectromagnetic interference (EMI) filter 660, which suppressesconducted interference, to an optical detector 640. The sensor 600further includes a controller 680 arranged to receive a light detectionsignal from the optical detector 640 and to control the opticalexcitation source 610 and the RF excitation source 630.

The RF excitation source 630 may be a microwave coil, for example. TheRF excitation source 630 is controlled to emit RF radiation with aphoton energy resonant with the transition energy between the groundm_(s)=0 spin state and the m_(s)=±1 spin states as discussed above withrespect to FIG. 3.

The optical excitation source 610 may be a laser or a light emittingdiode, for example, which emits light in the green, for example. Theoptical excitation source 610 induces fluorescence in the red, whichcorresponds to an electronic transition from the excited state to theground state. Light from the NV diamond material 620 is directed throughthe optical filter 650 to filter out light in the excitation band (inthe green for example), and to pass light in the red fluorescence band,which in turn is detected by the optical detector 640. The EMI filter660 is arranged between the optical filter 650 and the optical detector640 and suppresses conducted interference. The optical excitation lightsource 610, in addition to exciting fluorescence in the NV diamondmaterial 620, also serves to reset the population of the m_(s)=0 spinstate of the ground state ³A₂ to a maximum polarization, or otherdesired polarization.

The controller 680 is arranged to receive a light detection signal fromthe optical detector 640 and to control the optical excitation source610 and the RF excitation source 630. The controller may include aprocessor 682 and a memory 684, in order to control the operation of theoptical excitation source 610 and the RF excitation source 630. Thememory 684, which may include a nontransitory computer readable medium,may store instructions to allow the operation of the optical excitationsource 610 and the RF excitation source 630 to be controlled.

According to one embodiment of operation, the controller 680 controlsthe operation such that the optical excitation source 610 continuouslypumps the NV centers of the NV diamond material 620. The RF excitationsource 630 is controlled to continuously sweep across a frequency rangewhich includes the zero splitting (when the m_(s)=±1 spin states havethe same energy) photon energy of 2.87 GHz. When the photon energy ofthe RF radiation emitted by the RF excitation source 630 is thedifference in energies of the m_(s)=0 spin state and the m_(s)=−1 orm_(s)=+1 spin state, the overall fluorescence intensity is reduced atresonance, as discussed above with respect to FIG. 3. In this case,there is a decrease in the fluorescence intensity when the RF energyresonates with an energy difference of the m_(s)=0 spin state and them_(s)=−1 or m_(s)=+1 spin states. In this way the component of themagnetic field Bz along the NV axis may be determined by the differencein energies between the m_(s)=−1 and the m_(s)=+1 spin states.

As noted above, the diamond material 620 will have NV centers alignedalong directions of four different orientation classes, and thecomponent Bz along each of the different orientations may be determinedbased on the difference in energy between the m_(s)=−1 and the m_(s) =+1spin states for the respective orientation classes. In certain cases,however, it may be difficult to determine which energy splittingcorresponds to which orientation class, due to overlap of the energies,etc. The bias magnet 670 provides a magnetic field, which is preferablyuniform on the NV diamond material 620, to separate the energies for thedifferent orientation classes, so that they may be more easilyidentified.

FIG. 7 is a schematic illustrating a hydrophone 700 in accordance withsome illustrative implementations. In various implementations thecomponents of the hydrophone 700 can be contained within a housing 702.The hydrophone 700 includes a ferro-fluid 704 that is exposed. In thisimplementation, the hydrophone can be exposed to air, water, a fluid,etc. A magnet 708 activates the ferro-fluid 704. In someimplementations, the magnet 708 is strong enough to keep the ferro-fluid704 in place in the hydrophone. In other implementations, a membrane canbe used to contain the ferro-fluid 704. When activated the ferro-fluid704 forms a shape based upon the magnetic field from the magnet 708. Themagnet 708 can be a permanent magnet of an electro-magnet. As soundwaves hit the ferro-fluid 704, the shape of the ferro-fluid changes. Asthe ferro-fluid changes, the magnetic field from the ferro-fluid 704changes. One or more DNV sensors 706 can be used to detect these changesin the magnetic field. The magnetic field changes measured by the DNVsensors 706 can be converted into acoustic signals. For example, one ormore electric processors can be used to translate movement of theferro-fluid 704 into acoustic data. The hydrophone 700 can be used inmedical devices as well as within vehicles.

A reservoir (not shown) can be used to hold additional ferro-fluid. Asneeded, the ferro-fluid 704 that is being used to be detect sound wavescan be replenished by the additional ferro-fluid from the reservoir. Forexample, a sensor can detect how much ferro-fluid is currently beingused and control the reservoir to inject an amount of the additionalferro-fluid.

FIG. 8 is a schematic illustrating a portion of a vehicle 802 with ahydrophone in accordance with some illustrative implementations. Thecomponents of the hydrophone are similar to those described in FIG. 7. Aferro-fluid 804 is activated by a magnet 808. In this implementation,the ferro-fluid 804 is contained with a cavity 810. The magnet 808 isstrong enough such that the ferro-fluid 804 is contained within thecavity 810 even when the vehicle is moving. As the cavity 810 is notenclosed, the ferro-fluid 804 is exposed to the fluid in which thevehicle is traveling. For example, if the vehicle is a submarine, theferro-fluid 804 is exposed to the water. In other implementations, thevehicle travels in the air and the ferro-fluid 804 is exposed to air.

Prior to use, the ferro-fluid 804 can be stored in a container 812. Theferro-fluid 804 can then be injected into the cavity 810. In addition,during operation the amount of ferro-fluid 804 contained within thecavity 810 can be replenished with ferro-fluid from the container 812.

As sound waves contact the ferro-fluid 804, the ferro-fluid 804 changesshape. The change in shape can be detected by one or more DNV sensors806. In one implementation, a single DNV sensor can be used. In otherimplementations an array of DNV sensors can be used. For example,multiple DNV sensors can be place in a ring around the cavity 810.Readings from the DNV sensors 806 can be translated into acousticsignals.

FIG. 9 is a schematic illustrating a portion of a vehicle with ahydrophone with a containing membrane in accordance with someillustrative implementations. This implementation contains similarcomponents as to implementation illustrated in FIG. 8. What is differentis that a membrane 914 covers a portion of or the entire opening of thecavity 810. The membrane 914 can help enclose and contain theferro-fluid 804 within the cavity 810.

FIG. 10 is a schematic illustrating a portion of a vehicle with ahydrophone in accordance with some illustrative implementations. In thisimplementation, a ferro-fluid 104 is not contained within any cavity.Rather, the ferro-fluid 1004 is located outside of the vehicle. Themagnet 808 is used to contain the ferro-fluid 1004 in place. In oneimplementation, the magnet 808 is located within the vehicle. In otherimplementations, the magnet 808 is located outside of the vehicle. Inyet another implementation, a portion of the magnet 808 is locatedwithin the vehicle and a portion of the magnet 808 is located outside ofthe vehicle.

FIG. 11 is a schematic illustrating a portion of a vehicle with ahydrophone with a containing membrane in accordance with someillustrative implementations. Similar to FIG. 10, the ferro-fluid 1004is located outside of the vehicle. The ferro-fluid 1004 is enclosedwithin a membrane 1114 that contains the ferro-fluid 1004 near thevehicle. In this implementation, the magnet 808 can be used to containthe ferro-fluid 1004, but the combination of the magnet 808 and themembrane 1114 can be used to ensure that the ferro-fluid 1004 remainsclose enough to the vehicle to allow the DNV sensors to read the changesto the ferro-fluid 1004.

The foregoing description is provided to enable a person skilled in theart to practice the various configurations described herein. While thesubject technology has been particularly described with reference to thevarious figures and configurations, it should be understood that theseare for illustration purposes only and should not be taken as limitingthe scope of the subject technology. In some aspects, the subjecttechnology may be used in various markets, including for example andwithout limitation, advanced sensors and mobile space platforms.

There may be many other ways to implement the subject technology.Various functions and elements described herein may be partitioneddifferently from those shown without departing from the scope of thesubject technology. Various modifications to these embodiments may bereadily apparent to those skilled in the art, and generic principlesdefined herein may be applied to other embodiments. Thus, many changesand modifications may be made to the subject technology, by one havingordinary skill in the art, without departing from the scope of thesubject technology.

Phrases such as an aspect, the aspect, another aspect, some aspects, oneor more aspects, an implementation, the implementation, anotherimplementation, some implementations, one or more implementations, anembodiment, the embodiment, another embodiment, some embodiments, one ormore embodiments, a configuration, the configuration, anotherconfiguration, some configurations, one or more configurations, thesubject technology, the disclosure, the present disclosure, othervariations thereof and alike are for convenience and do not imply that adisclosure relating to such phrase(s) is essential to the subjecttechnology or that such disclosure applies to all configurations of thesubject technology. A disclosure relating to such phrase(s) may apply toall configurations, or one or more configurations. A disclosure relatingto such phrase(s) may provide one or more examples. A phrase such as anaspect or some aspects may refer to one or more aspects and vice versa,and this applies similarly to other foregoing phrases

A reference to an element in the singular is not intended to mean “oneand only one” unless specifically stated, but rather “one or more.” Theterm “some” refers to one or more. Underlined and/or italicized headingsand subheadings are used for convenience only, do not limit the subjecttechnology, and are not referred to in connection with theinterpretation of the description of the subject technology. Allstructural and functional equivalents to the elements of the variousembodiments described throughout this disclosure that are known or latercome to be known to those of ordinary skill in the art are expresslyincorporated herein by reference and intended to be encompassed by thesubject technology. Moreover, nothing disclosed herein is intended to bededicated to the public regardless of whether such disclosure isexplicitly recited in the above description.

What is claimed is:
 1. A hydrophone comprising: a ferro-fluid configured to deform when contacted by sound waves; a magnet configured to activate the ferro-fluid; at least one diamond nitrogen vacancy (DNV) sensor configured to detect the magnetic field of the ferro-fluid and to detect movement of the ferro-fluid; and an electronic processor configured to translate movement of the ferro-fluid into acoustic data associated with the sound waves.
 2. The hydrophone of claim 1, wherein the magnet is strong enough to keep the ferro-fluid contained within the hydrophone.
 3. The hydrophone of claim 1, further comprising a membrane configured to enclose the ferro-fluid and contain the ferro-fluid within the hydrophone.
 4. The hydrophone of claim 1, wherein the magnet is a permanent magnet.
 5. The hydrophone of claim 1, wherein the magnet is an electro-magnet.
 6. The hydrophone of claim 1, wherein the at least one DNV sensor comprises two or more DNV sensors.
 7. The hydrophone of claim 1, wherein the at least one DNV sensor consists of one DNV sensor.
 8. The hydrophone of claim 1, further comprising a ferro-fluid reservoir configured to contain additional ferro-fluid.
 9. The hydrophone of claim 8, wherein the ferro-fluid reservoir is configured to replenish the ferro-fluid of the hydrophone with at least a portion of the additional ferro-fluid.
 10. A vehicle containing hydrophone, the vehicle comprising: the hydrophone comprising: a ferro-fluid that is configured to deform when contacted by sound waves; a magnet configured to activate the ferro-fluid; at least one diamond nitrogen vacancy (DNV) sensor configured to detect the magnetic field of the ferro-fluid and to detect movement of the ferro-fluid; and an electronic processor configured to translate movement of the ferro-fluid into acoustic data associated with the sound waves; and a cavity configured to contain the ferro-fluid.
 11. The vehicle of claim 10, wherein the magnet is strong enough to keep the ferro-fluid contained within the hydrophone.
 12. The vehicle of claim 10, wherein the hydrophone further comprises a membrane configured to enclose the ferro-fluid and contain the ferro-fluid within the cavity.
 13. The vehicle of claim 10, wherein the magnet is a permanent magnet.
 14. The vehicle of claim 10, wherein the magnet is an electro-magnet.
 15. The vehicle of claim 10, wherein the at least one DNV sensor comprises two or more DNV sensors.
 16. The vehicle of claim 10, wherein the at least one DNV sensor consists of one DNV sensor.
 17. A vehicle containing hydrophone, the vehicle comprising: the hydrophone comprising: a ferro-fluid that is configured to deform when contacted by sound waves and located outside of the vehicle; a magnet configured to activate the ferro-fluid; at least one diamond nitrogen vacancy (DNV) sensor configured to detect the magnetic field of the ferro-fluid and to detect movement of the ferro-fluid; and an electronic processor configured to translate movement of the ferro-fluid into acoustic data associated with the sound waves.
 18. The vehicle of claim 17, wherein the magnet is strong enough to keep the ferro-fluid contained outside of the vehicle.
 19. The vehicle of claim 17, wherein the hydrophone further comprises a membrane configured to enclose the ferro-fluid and contain the ferro-fluid within the cavity.
 20. The vehicle of claim 17, wherein the magnet is a permanent magnet.
 21. The vehicle of claim 17, wherein the magnet is an electro-magnet.
 22. The vehicle of claim 17, wherein the at least one DNV sensor comprises two or more DNV sensors.
 23. The vehicle of claim 17, wherein the at least one DNV sensor consists of one DNV sensor. 